Scale this up or down by how it looks but basically:
3 parts Flourite (Similar to aquatic plant soil 'APS')
1 part 1/8" - 3/16" chicken grit
1 part crushed coral
1 part pool filter sand
1 tablespoon of dolomite lime per gallon of mix.
Flourite and crushed coral is available at petco or petsmart or your local pet store.
I use the Redstone chicken grit available at DIY centers or tractor supply stores.
I need to repot my gigantea to this, or take a couple leaf pulls to see how it does.
I use the HTH pool filter sand available through Ace Hardware.